Add a stop gap to Sema::CorrectTypo() to correct only up to 20 typos.

This is to address a serious performance problem observed when running
'clang -fsyntax-only' on really broken source files.  In one case,
repeatedly calling CorrectTypo() caused one source file to be rejected
after 2 minutes instead of 1 second.

This patch causes typo correction to take neglible time on that file
while still providing correction results for the first 20 cases.  I
felt this was a reasonable number for moderately broken source files.

I don't claim this is the best solution.  Comments welcome.  It is
necessary for us to address this issue because it is a serious
performance problem.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95049 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 1 deletions

diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 95f0d318de..d1a379435e 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -2348,9 +2348,16 @@ void TypoCorrectionConsumer::FoundDecl(NamedDecl *ND, NamedDecl *Hiding,
 bool Sema::CorrectTypo(LookupResult &Res, Scope *S, const CXXScopeSpec *SS,
                        DeclContext *MemberContext, bool EnteringContext,
                        const ObjCObjectPointerType *OPT) {
-  
   if (Diags.hasFatalErrorOccurred())
     return false;
+
+  // Provide a stop gap for files that are just seriously broken.  Trying
+  // to correct all typos can turn into a HUGE performance penalty, causing
+  // some files to take minutes to get rejected by the parser.
+  // FIXME: Is this the right solution?
+  if (TyposCorrected == 20)
+    return false;
+  ++TyposCorrected;
   
   // We only attempt to correct typos for identifiers.
   IdentifierInfo *Typo = Res.getLookupName().getAsIdentifierInfo();